1. Field of the Invention:
This invention generally relates to circuit interrupter apparatus and, more particularly, to an operating mechanism for such apparatus having an improved chemical operator drive mechanism of the double-action type.
2. Description of the Prior Art:
Certain types of circuit interrupters are provided with operating drive mechanisms that employ a chemical operator drive means comprising a gas generator of the chemical propellant type which ignites a propellant charge of gas-generating material and directs a high pressure gaseous medium into a drive piston and power cylinder assembly. The piston is coupled by suitable linkage means to the movable contact of the interrupter and the operating mechanism and is adapted to open and close the contacts in a rapid and positive manner when the propellant charges are ignited.
Circuit interrupter apparatus having a chemical operator drive means arranged to close the interrupter contacts is disclosed in U.S. Pat. No. 4,131,774 issued Dec. 26, 1978 to Crookston et al. A circuit breaker having a gas-propellant type operating means for quickly opening the breaker contacts and utilizing spring means for returning the actuating piston to its closed-contact position is disclosed in U.S. Pat. No. 4,271,341 issued June 2, 1981 to Meyer.
While the prior art chemical operator drive systems provide the desired quick-response actuation of the circuit breaker operating mechanism and contacts, they employ piston rods that are sealed to the cylinder of the operator assembly. These seals not only added to the cost of the circuit breaker but constitute a maintenance problem insofar as the combustion of the propellant inherently produces residues which are deposited on the piston drive rod with resultant "gumming" of the shaft seal and progressive abrasion of both the piston seal and shaft. It would accordingly be desirable from both a cost and reliability standpoint to eliminate the need for shaft seals in chemical operator drive mechanisms without detracting from the quick-response and positive-acting characteristics of the drive mechanisms.